<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>
<body>
    
</body>
<style>
    body{
        min-height: 400px;
        background-size: cover;
    }
</style>
<script>
    var arr = ["src/images/15532327436_74c32632ac_k.jpg", "src/images/32735073444_83b7a691dc_k.jpg",  "src/images/34378167170_be43601df6_k.jpg"];
    var index = Math.floor(Math.random() * arr.length);
    document.body.style.backgroundImage = "url("+ arr[index]+")";
</script>
</html>